1. Field of the Invention
The present invention relates generally to fuel injection systems and more specifically to fuel injection systems for engine which are adapted to run different fuels or a mixture of different fuels.
2. Description of the Prior Art
In commonly used fuel injection systems the basic fuel injection pulse width is determined by sensing the amount of air Q being induced into the engine (i.e. engine load) and the engine speed N, and using this data in the following equation: EQU Tp=K.times.Q/N (1)
where K is a constant
After having obtained the basic fuel injection pulse width Tp, a final injection pulse width Ti is derived by applying a correction factor COEF which takes various driving conditions into account. Viz.: EQU Ti=2.times.(Tp.times.COEF.times. )+Ts (2)
where is a air-fuel ratio feedback correction coefficient, and Ts is a correction factor which takes the rise time of the fuel injectors into account. An example of such a concept is disclosed in JU-A-62-162364.
COEF is a derived by summing a plurality of individual correction values. Viz.: EQU COEF=1+KMR+KTW+KAS+Kfuel-Kdc (3)
where:
KMR is carburettion ratio correction factor based on the engine speed and the basic engine pulse width--Under high engine load or speed, the value assumes a large value;
KTW is correction factor which varies with the engine coolant temperature;
KAS is an engine cranking and initial engine starting correction factor which varies with the engine coolant temperature at the time the engine switch is closed and the ignition key is turned to the ON position;
Kfuel is an acceleration correction factor which varies with the amount of change in the throttle valve position; and
KDC is a low speed low amount correction factor.
JP-A-56-98540 discloses a fuel injection arrangement is adapted to permit the fuel which is supplied to the engine is switched from gasoline to alcohol or the engine is operated on a mixture of alcohol and gasoline.
This system includes a alcohol sensor which detects the amount of alcohol which is present in the fuel being supplied to the fuel injectors of the engine. In this case the final injection pulse width is calculated using the following equation: EQU Ti=2.times.(Tp.times.COEF.times.KMET.times. )+Ts (4)
wherein KMET is a correction factor which varies with the amount of alcohol detected in the fuel. In this instance the value of KMET varies in the manner shown in FIG. 5.
However, this system has suffered from the drawback that in the event that the alcohol sensor malfunctions, the erroneous alcohol content indication adversely effects the fuel injection pulse width.
When the engine is operating in a power zone at high speed or under high load the value of KMR has been increased to a large value in order to obtain the required power output. However, if the value of KMR should be arbitrarily increased due to sensor malfunction, when the vehicle is not operating under high speed/load conditions, the value of Ti becomes abnormally high and too much fuel is injected into the engine. This results in the air-fuel ratio becoming excessively rich and gives rise to a loss in fuel economy and emission control. In the worst case the loss of air-fuel ratio control can lead to engine stalling and the like.